[Cerowrt-devel] SQM Question #5: Link Layer Adaptation Overheads

Fred Stratton fredstratton at imap.cc
Sat Jan 4 13:40:49 EST 2014

Link Names:

For consistency, if ADSL is used as a portmanteau term, them VDSL should 
be used as the equivalent for VDSL and VDSL2.

CeroWRT has to decide whether it is an experimental build, or something 
that will eventually be used in production, so these decisions can be 
made consistently.

I concur with your ADSL setup suggestion as default. I have been running 
the Sebastian Moeller ping script overnight to calculate ADSL overhead 
for the last several days. After several hours of curve fitting using 
Octave, an overhead result is displayed. This novel approach works well.

The overhead for the particular setup I use was 40 for PPPoE, and 10 for 

The default you suggest is a suitable starting point, I suggest.

On 04/01/14 18:16, Rich Brown wrote:
> QUESTION #5: I still don’t have any great answers for the Link Layer Adaptation overhead descriptions and recommendations. In an earlier message, (see https://lists.bufferbloat.net/pipermail/cerowrt-devel/2013-December/001914.html and following messages), Fred Stratton described the overheads carried by various options, and Sebastian Moeller also gave some useful advice.
> After looking at the options, I despair of giving people a clear recommendation that would be optimal for their equipment. Consequently, I believe the best we can do is come up with “good enough” recommendations that are not wrong, and still give decent performance.
> In this spirit, I have changed Draft #3 of the “Setting up SQM” page to reflect this understanding. See http://www.bufferbloat.net/projects/cerowrt/wiki/Setting_up_AQM_for_CeroWrt_310
> 	ADSL/ATM link: Choose “ADSL/ATM", and set Per Packet Overhead to 40
> 	VDSL2 link: Choose “VDSL”, and set Per Packet Overhead to 8
> 	Other kind of link (e.g., Cable, Fiber, Ethernet, other not listed): Choose “None (default)”, and set Per Packet Overhead to 0
> NB: I have changed the first menu choice to “ADSL/ATM” and the second to “VDSL” in the description. I would ask that we change to GUI to reflect those names as well. This makes it far easier/less confusing to talk about the options.
> As always, I welcome help in setting out clear recommendations that work well for the vast majority of people who try CeroWrt. Thanks.
> Rich
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